/*
 * Copyright 2012-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package rewards;

import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.allOf;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import java.util.ArrayList;
import java.util.List;

import org.hamcrest.Matcher;
import org.junit.jupiter.api.extension.AfterEachCallback;
import org.junit.jupiter.api.extension.BeforeEachCallback;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.api.extension.ExtensionContext;
import org.junit.jupiter.api.extension.ExtensionContext.Namespace;
import org.junit.jupiter.api.extension.ExtensionContext.Store;
import org.junit.jupiter.api.extension.ParameterContext;
import org.junit.jupiter.api.extension.ParameterResolver;
import org.junit.platform.commons.support.ReflectionSupport;

/**
 * {@code @CaptureSystemOutput} is a JUnit JUpiter extension for capturing
 * output to {@code System.out} and {@code System.err} with expectations
 * supported via Hamcrest matchers.
 * 
 * <h4>Example Usage</h4>
 * 
 * <pre style="code">
 * {@literal @}Test
 * {@literal @}CaptureSystemOutput
 * void systemOut(OutputCapture outputCapture) {
 *     outputCapture.expect(containsString("System.out!"));
 *
 *     System.out.println("Printed to System.out!");
 * }
 * 
 * {@literal @}Test
 * {@literal @}CaptureSystemOutput
 * void systemErr(OutputCapture outputCapture) {
 *     outputCapture.expect(containsString("System.err!"));
 *
 *     System.err.println("Printed to System.err!");
 * }
 * </pre>
 *
 * <p>Based on code from Spring Boot's
 * <a href="https://github.com/spring-projects/spring-boot/blob/d3c34ee3d1bfd3db4a98678c524e145ef9bca51c/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/rule/OutputCapture.java">OutputCapture</a>
 * rule for JUnit 4 by Phillip Webb and Andy Wilkinson.
 * 
 * @author Sam Brannen
 * @author Phillip Webb
 * @author Andy Wilkinson
 */
@Target({ TYPE, METHOD })
@Retention(RUNTIME)
@ExtendWith(CaptureSystemOutput.Extension.class)
public @interface CaptureSystemOutput {

	class Extension implements BeforeEachCallback, AfterEachCallback, ParameterResolver {

		@Override
		public void beforeEach(ExtensionContext context) throws Exception {
			getOutputCapture(context).captureOutput();
		}

		@Override
		public void afterEach(ExtensionContext context) throws Exception {
			OutputCapture outputCapture = getOutputCapture(context);
			try {
				if (!outputCapture.matchers.isEmpty()) {
					String output = outputCapture.toString();
					assertThat(output, allOf(outputCapture.matchers));
				}
			}
			finally {
				outputCapture.releaseOutput();
			}
		}

		@Override
		public boolean supportsParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
			boolean isTestMethodLevel = extensionContext.getTestMethod().isPresent();
			boolean isOutputCapture = parameterContext.getParameter().getType() == OutputCapture.class;
			return isTestMethodLevel && isOutputCapture;
		}

		@Override
		public Object resolveParameter(ParameterContext parameterContext, ExtensionContext extensionContext) {
			return getOutputCapture(extensionContext);
		}

		private OutputCapture getOutputCapture(ExtensionContext context) {
			return getOrComputeIfAbsent(getStore(context), OutputCapture.class);
		}

		private <V> V getOrComputeIfAbsent(Store store, Class<V> type) {
			return store.getOrComputeIfAbsent(type, ReflectionSupport::newInstance, type);
		}

		private Store getStore(ExtensionContext context) {
			return context.getStore(Namespace.create(getClass(), context.getRequiredTestMethod()));
		}

	}

	/**
	 * {@code OutputCapture} captures output to {@code System.out} and {@code System.err}.
	 * 
	 * <p>To obtain an instance of {@code OutputCapture}, declare a parameter of type
	 * {@code OutputCapture} in a JUnit Jupiter {@code @Test}, {@code @BeforeEach},
	 * or {@code @AfterEach} method.
	 * 
	 * <p>{@linkplain #expect Expectations} are supported via Hamcrest matchers.
	 * 
	 * <p>To obtain all output to {@code System.out} and {@code System.err}, simply
	 * invoke {@link #toString()}.
	 *
	 * @author Phillip Webb
	 * @author Andy Wilkinson
	 * @author Sam Brannen
	 */
	static class OutputCapture {

		private final List<Matcher<? super String>> matchers = new ArrayList<>();

		private CaptureOutputStream captureOut;

		private CaptureOutputStream captureErr;

		private ByteArrayOutputStream copy;

		void captureOutput() {
			this.copy = new ByteArrayOutputStream();
			this.captureOut = new CaptureOutputStream(System.out, this.copy);
			this.captureErr = new CaptureOutputStream(System.err, this.copy);
			System.setOut(new PrintStream(this.captureOut));
			System.setErr(new PrintStream(this.captureErr));
		}

		void releaseOutput() {
			System.setOut(this.captureOut.getOriginal());
			System.setErr(this.captureErr.getOriginal());
			this.copy = null;
		}

		private void flush() {
			try {
				this.captureOut.flush();
				this.captureErr.flush();
			}
			catch (IOException ex) {
				// ignore
			}
		}

		/**
		 * Verify that the captured output is matched by the supplied {@code matcher}.
		 *
		 * <p>Verification is performed after the test method has executed.
		 *
		 * @param matcher the matcher
		 */
		public void expect(Matcher<? super String> matcher) {
			this.matchers.add(matcher);
		}

		/**
		 * Return all captured output to {@code System.out} and {@code System.err}
		 * as a single string.
		 */
		@Override
		public String toString() {
			flush();
			return this.copy.toString();
		}

		private static class CaptureOutputStream extends OutputStream {

			private final PrintStream original;

			private final OutputStream copy;

			CaptureOutputStream(PrintStream original, OutputStream copy) {
				this.original = original;
				this.copy = copy;
			}

			PrintStream getOriginal() {
				return this.original;
			}

			@Override
			public void write(int b) throws IOException {
				this.copy.write(b);
				this.original.write(b);
				this.original.flush();
			}

			@Override
			public void write(byte[] b) throws IOException {
				write(b, 0, b.length);
			}

			@Override
			public void write(byte[] b, int off, int len) throws IOException {
				this.copy.write(b, off, len);
				this.original.write(b, off, len);
			}

			@Override
			public void flush() throws IOException {
				this.copy.flush();
				this.original.flush();
			}

		}

	}

}
